The research is part of DARPA's Information in a Photon program which is looking to discover and take advantage of the basic information content carrying capabilities of a photon and exploit this information capacity for imaging/sensing and communications applications, the agency stated.

The program features communications and imaging components. In the communications area research will be directed toward maximizing the information content of every transmitted/received photon in a free-space optical (FSO) communication system. "Recent progress on the information capacity of optical communications has largely focused on novel 'spectrally dense modulation' techniques for increasing the spectral information efficiency of these channels. Recent demonstrations approaching 10 bits/sec/Hz in fiber suggest that similar techniques may also be successfully employed for FSO applications," DARPA stated.

It is in this area that BBN will focus part of its efforts. In a project it calls Photon Information Efficient Communications, BBN wants to create techniques that increase the current limits of optical communications technology while approaching the ultimate limits of photon information efficiency. The idea is to significantly increase power management, speed and reach on free space optical communication links, including far-field links used in deep space, BBN stated.

The company will generate and demonstrate experimental technologies, such as multiple-spatial-mode design and adaptive joint-detection receivers that attain communications at 10-bits per photon and 5-bits/sec/Hz while simultaneously encoding information in space and time, BBN stated.

"We are developing techniques that greatly improve the performance of current optical communications and approach the quantum limits of light's information carrying capacity," said Saikat Guha, a Raytheon BBN Technologies scientist in a statement.

A second BBN project, Fundamental Information Capacity of Electromagnetism with Squeezing and Spatial Entanglement, looks to determine the theoretical performance limits for imaging technology as determined by the laws of quantum physics. In collaboration with the University of Virginia, Raytheon BBN Technologies will conduct a theoretical and experimental program of study investigating newly engineered quantum states of light to perform imaging with performance superior to conventional techniques.

"Conventional imaging techniques use classical light pulses from lasers and detect the resulting reflection from a target or scene," said Jonathan Habif, Raytheon BBN Technologies senior scientist. "We have set out to define new quantum states of light and subsequent detection methods from which we can obtain far more image information from a lot less light."

DARPA says: "Conventional wisdom suggests that an image requires more than 1000 photons per pixel in order to be useful. This traditional rule-of-thumb, when combined with a desire for ever-increasing pixel-counts, can result in large apertures and/or long integration times which in turn increase both complexity such as the need for stabilization and/or size, weight and power costs.

It is apparent that current imaging systems under-utilize photon information capacity. Consider a natural scene that is imaged using an 8 bit per pixel focal plane. With a requirement to collect 1000 photons per pixel we see that such a system achieves a photon efficiency of 125 photons per bit or 8e-3 bits per photon (bpp). Because of the redundancy that is characteristic of natural imagery, it is not uncommon for such a scene to be visually indistinguishable after compression by 10x, suggesting an even lower photon information efficiency of 8e-4 bpp. Drastically increasing this photon efficiency will provide revolutionary capabilities for imaging platforms."